Paramedics are said to be "seriously concerned" that closing Blackpool and Blackburn service centres and moving the work to Preston will mean vehicles are off the road for longer, adding to already lengthy delays in reaching emergency call-outs.
Neil Cosgrove, branch secretary for the Unite union, said the plans by the North West Ambulance Service (NWAS) to merge its three Lancashire depots at Broughton would "create a monster that is doomed to fail."
"Vehicles are having to travel further to have their planned services and safety inspections and there are now longer delays as ambulances cannot be serviced in the allotted time because of the reduced capacity," he said.
‘How a car crash saved my life’: Royal Preston patient recalls chance cancer diagnosis as hospital’s major trauma centre marks tenth anniversary
Lancashire dental crisis: Fulwood dental surgery Dentistry by Cure Clinics is offering free checkups this month
Lancashire’s NHS dental crisis: Chorley resident blasts “sick joke” of an advert boasting about the number of NHS dentists
‘No guarantees’ over Lancashire blood test hub as pathology collaboration boss announces retirement
Freckleton care home where grandma, 91, was beaten to death is placed in special measures again after 'inadequate' CQC report
"This means a potential delay in vehicles being available for crews to respond to emergency calls. We are already seeing massive delays in patients waiting and this will further exacerbate the problem.
"This is an important issue. The public need to be made aware of the absolutely terrible situation we are in. We are struggling.
"Ultimately it could cost lives. If they (NWAS) don't get their act together then sadly I think people could die."
The plan to bring the ambulance workshops at Blackpool and Blackburn into Broughton on a permanent basis is being opposed by both the Unite and Unison trade unions who represent ambulance staff.
Blackpool technicians have been working at the Preston site since May on a "temporary" basis because the new ambulance super station being developed in Waterloo Road does not have facilities.
Blackpool used to have four ramps for vehicle inspections, Blackburn have five and Broughton six. The union claims that by centralising workshops at Broughton the service will lose nine of those 15 ramps.
NWAS has been outsourcing some of the work to main dealers because they cannot meet the demand. But the union claims vehicles have been returning with serious defects, taking up further time for in-house technicians to put them right.
The unions say NWAS is also changing working patterns including longer shifts on a seven day rota.
"These staff are working to full capacity and there is no slack in the system to allow for training, annual leave and sickness, whilst maintaining the existing pressures being placed on them or the service plans," said Neil Cosgrove.
"In principle, staff are ready to embrace change and are prepared to adopt these changes to their terms and conditions. However, since this plan was first mooted in 2017, staff have raised concerns about how this move can be achieved, as the footprint of the Broughton site will not increase to accommodate the increase in throughput of vehicles.
"There are also serious health and safety concerns, affecting not only the workshop but the whole of the Broughton site. Despite raising them, senior management have failed to address them to an appropriate level.
"Prior to 2017, the trust centralised the fleet workshops for the Cheshire and Mersey area. This is an acquired new build with excellent facilities, with the Wallasey site remaining open to accommodate the needs in the Wirral/Cheshire area.
"There is a future proposal to build a brand new workshop in the Greater Manchester area, as the existing one on longer meets the needs of the service.
"But in Lancashire, we are expected to squeeze a quart into a pint pot.
"The current facilities are not fit for purpose and requests for a new build to accommodate these changes in a positive way have fallen on deaf ears.
"Staff are at breaking point and are actively looking for alternative employment. We have already seen staff leave because of these proposals.
"They love the work they do and feel they are doing their part in providing a service to the patients of Lancashire and South Cumbria, but they are no longer prepared to sit and wait for the senior management of NWAS to create a monster that is doomed to fail. And at what cost?
"We feel it is time that the public of Lancashire and the wider area are made aware of what is happening within their ambulance service and how this will impact on their care."
The North West Ambulance Service has been approached for a response.